import { type FSWatcher, watch } from "node:fs";

const DEBOUNCE_MS = 150;

/**
 * Watches a set of local directories with node's fs.watch and fires onChange
 * (debounced per dir — fs.watch emits bursts) when their contents change. Used
 * to auto-refresh the active tab's local panels instantly; SFTP has no
 * equivalent, so remote panels are polled UI-side instead.
 *
 * onChange is late-bound (assigned after the RPC exists, like AppDeps.events)
 * so it can push pathRefresh to the main webview.
 */
export class LocalDirWatcher {
	onChange: (dir: string) => void = () => {};
	private readonly handles = new Map<string, FSWatcher>();
	private readonly debounces = new Map<string, ReturnType<typeof setTimeout>>();

	/** Replace the watched set: drop handles no longer wanted, open new ones. */
	setWatched(dirs: string[]): void {
		const wanted = new Set(dirs);
		for (const [dir, handle] of this.handles) {
			if (!wanted.has(dir)) {
				handle.close();
				this.handles.delete(dir);
			}
		}
		for (const dir of wanted) {
			if (this.handles.has(dir)) continue;
			try {
				const handle = watch(dir, () => this.fire(dir));
				// a watched dir that gets deleted/unmounted errors — just drop it
				handle.on("error", () => this.drop(dir));
				this.handles.set(dir, handle);
			} catch {
				// dir vanished between listing and watching — ignore
			}
		}
	}

	private fire(dir: string): void {
		const pending = this.debounces.get(dir);
		if (pending) clearTimeout(pending);
		this.debounces.set(
			dir,
			setTimeout(() => {
				this.debounces.delete(dir);
				this.onChange(dir);
			}, DEBOUNCE_MS),
		);
	}

	private drop(dir: string): void {
		this.handles.get(dir)?.close();
		this.handles.delete(dir);
	}

	dispose(): void {
		for (const handle of this.handles.values()) handle.close();
		this.handles.clear();
		for (const pending of this.debounces.values()) clearTimeout(pending);
		this.debounces.clear();
	}
}